Generally, launch vehicles are comprised of a booster stage that provides the initial boost towards orbit. In addition, an upper stage is often employed to carry a payload to a further desired orbit or to achieve escape velocity. Commonly, upper stages are powered by rocket motors that are fed by cryogenic fuels and oxidizers, such as liquid hydrogen (LH2) and liquid oxygen (LO2). Alternatively, other propellants known to those of skill in the art, such as hydrazine (N2H4), may be used. After orbit insertion or a desired escape velocity is achieved, the payload is separated from the upper stage by way of methods which are well known by those of skill in the art. The payload may have its own propulsion system or propulsion module to control its position and altitude. An example of a booster stage and upper stage combination is the Atlas V launch vehicle and the Centaur upper stage manufactured by either the United Launch Alliance (ULA), the assignee of the instant application, or the Lockheed Martin Corporation. One skilled in the art will appreciate that other launch vehicles employ upper stages, such as the Delta II and the Delta IV launch systems manufactured by either the ULA or the Boeing Corporation.
The upper stage is generally provided with a quantity of propellant which is greater than what is required to perform a mission. The additional propellant is used to help stabilize the upper stage propellant tanks and provide propellant to accommodate unforeseen mission deviations. After the payload has achieved orbit and separated from the upper stage, normally all residual propellant is expelled in a process called “blow down” to “safe the stage.” Blow down refers to venting upper stage residual propellant material, possibly through the upper stage rocket motor. Safing the stage refers to minimizing the potential of future risk of the stage coming apart and causing additional space debris.
It will be apparent to those of skill in the art that in order to provide sufficient propellant for deep space exploration or to allow heavy payloads to be delivered to higher energy orbits than their launch vehicles would otherwise permit, it may be highly advantageous to undergo refueling in space. For example, space exploration and colonization visionaries foresee the use of orbiting depots that are used to fuel or refuel upper stages and/or payloads (some payloads are capable of independent propulsion and therefore have independent propellant requirements). The ability to fuel a rocket or engine in orbit has the advantage of decreasing the launch weight of launch vehicles, thereby increasing performance of those launch vehicles, increasing safety and decreasing costs associated with the launch. The Orbital Express space mission is one example of a system that is designed to refuel/service a payload in space. The Orbital Express mission generally comprised two spacecraft, an Autonomous Space Transport Robotic Orbiter (ASTRO), and a next generation satellite. ASTRO established the technical feasibility of an autonomous on-orbit refueling and reconfiguration of the next generation satellite. Furthermore, U.S. Pat. No. 5,862,670 to Lak, the entire disclosure of which is incorporated by reference herein, describes a system wherein upper stage propellant is stored in the cargo bay of the space shuttle, launched into space by a booster stage, and is used to fuel the space shuttle or other payloads to reduce ground handling of the volatile cryogenic upper stage propellants.
It has been long appreciated that certain portions of a launch vehicle are not effectively used. One example of efforts to utilize available space is the Ariane Structure for Auxiliary Payloads (ASAP) launch vehicle. ASAP is positioned in the upper stage of the launch vehicle and may carry multiple payloads. The upper stage or primary payload delivery system positions the primary payload for deployment. Once the primary payload is deployed, the ASAP launcher deploys the one or more secondary payloads and maneuvers between deployment as is needed using its own propulsion system or propulsion module. Another example of increased utilization of space is a payload adapter ring (or “adapter”) interconnected to the upper stage and designed for supporting a payload. The space internal to the ring and between the ring and a payload fairing of the upper stage has been used to accommodate additional payloads, i.e., “secondary payloads.” One example of such a ring is the Evolved Expendable Launch Vehicle (EELV) Secondary Payload Adaptor (ESPA). Secondary payloads are generally separated from the adapter ring subsequent to primary payload separation. Secondary payloads may be designed to be used for a limited time until their orbits decay and they are destroyed during re-entry or may be designed for a more extended lifetime. Further, as previously noted, some secondary payloads are capable of independent propulsion and include propulsion systems, such as thrusters and control modules, that allow the secondary payload to maintain a desired orbit or to achieve escape velocity. None of the launch systems currently in existence or otherwise known to those of skill in the art, however, disclose a method of filling a propellant tank associated with a payload delivery system or a payload propulsion system subsequent to launch and in space.
NASA's Lunar Crater Observation and Sensing Satellite (LCROSS) includes a propellant tank that is situated inside a payload adapter ring that is positioned between the upper stage and the primary payload. The payload adapter ring also provides mounting positions for avionics and hydrazine thrusters. However, the propellant tank is filled with hydrazine prior to launch. After separation from the booster stage, the upper stage launches the primary payload (LRO) and the secondary payload (LCROSS) on a trajectory towards the moon. Thereafter, the secondary payload, which includes the payload adapter ring, a secondary payload delivery system comprising a propellant tank, avionics and propulsion module, and perhaps one or more other modules containing test or experimental apparatus, is separated from the upper stage. The upper stage then impacts the lunar surface forcing lunar dust into space that is collected and analyzed by one or more of the other modules of the LCROSS. Importantly, the propulsion system of the LCROSS does not utilize propellant residuals of the upper stage.
Thus, there is a long felt and unresolved need to utilize the residual upper stage propellant to fuel a payload delivery system which includes one or more payload propulsion systems. For convenience purposes, such an on-orbit payload delivery system is called OPADS (Orbital Payload Delivery System). The concept embodies the transfer and use of any upper stage propellant (e.g., LH2, LO2, RP1, MMH, NTO, etc) and is not limited to any single propellant such as LH2. The following disclosure describes some, but not all, embodiments of the OPADS wherein residual propellant from the upper stage is transferred to a propellant tank that is launched empty and is used by one or more payloads and/or payload propulsion modules.